A systematic review of the international evidence on the effectiveness of COVID-19 mitigation measures in communal rough sleeping accommodation

Abstract Background Accommodations with shared washing facilities increase the risks of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection for people experiencing rough sleeping and evidence on what interventions are effective in reducing these risks needs to be understood. Methods Systematic review, search date 6 December 2022 with methods published a priori. Electronic searches were conducted in MEDLINE, PubMed, Cochrane Library, CINAHL and the World Health Organization (WHO) COVID-19 Database and supplemented with grey literature searches, hand searches of reference lists and publication lists of known experts. Observational, interventional and modelling studies were included; screening, data extraction and risk of bias assessment were done in duplicate and narrative analyses were conducted. Results Fourteen studies from five countries (USA, England, France, Singapore and Canada) were included. Ten studies were surveillance reports, one was an uncontrolled pilot intervention, and three were modelling studies. Only two studies were longitudinal. All studies described the effectiveness of different individual or packages of mitigation measures. Conclusions Despite a weak evidence base, the research suggests that combined mitigation measures can help to reduce SARS-CoV-2 transmission but are unlikely to prevent outbreaks entirely. Evidence suggests that community prevalence may modify the effectiveness of mitigation measures. More longitudinal research is needed. Systematic review registration PROSPERO CRD42021292803.


Introduction
People are defined as sleeping rough if they sleep outside or without adequate shelter. 1 A higher prevalence of comorbidities, 2 and lower vaccination rates than the general population, [3][4][5][6][7] make people experiencing rough sleeping more vulnerable to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, coronavirus disease 2019 (COVID-19) complications and other nonrespiratory infections such as tuberculosis. 8In March 2020, the 'everyone in initiative' was launched to help people experiencing rough sleeping in England to comply with COVID-19 regulations. 9To this aim, additional funding was made available for accommodation providers to provide more single occupancy accommodation or to restructure existing accommodations to make them COVID-19-safe (i.e.allow isolation).
To help people experiencing rough sleeping to better adhere to personal protective measures, the UK government maintains that single-occupancy accommodation should be provided wherever possible. 10owever, in some situations, the need for temporary accommodation for people experiencing rough sleeping may exceed single occupancy availability, and communal facilities may still be needed. 10,11any of the communal accommodations for people who sleep rough in England typically have shared washing facilities, whilst other aspects such as kitchen use or sleeping arrangements may vary. 11Thus, 'communal accommodation' for people experiencing rough sleeping within England can be defined as accommodations that have shared washing facilities (e.g.bathrooms).
Communal accommodation increases the risk of COVID-19 outbreaks, 12,13 which are defined as two or more testconfirmed cases associated with a specific context within 14 days. 14Hence, when communal accommodation is the only option, promotion of vaccinations, improved ventilation, mask-wearing, limiting close contact and frequent hand washing are recommended by the UK government. 10owever, during the pandemic, most communal accommodations in England were closed; 15 therefore, the effectiveness of these measures in communal accommodations is unclear.Understanding the efficacy of mitigation strategies in this setting is essential for effective future planning and implementation of guidance and policies intending to protect people experiencing rough sleeping against COVID-19 and other infections.This paper thus systematically reviews the international evidence on the effectiveness of measures to prevent the spread of SARS-CoV-2 infection in accommodations for people experiencing rough sleeping that have shared washing facilities.

Methods
This systematic review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines 16 and was registered with PROSPERO.Review protocol registration number: CRD42021270053.

Search strategy, selection criteria and screening process
Five electronic databases: MEDLINE, PubMed, Cochrane Library, CINAHL and the WHO COVID-19 Database were searched from database establishment to the 6 December 2022.By combining 'COVID-19', 'transmission' and 'setting or population' terms, searches were restricted to research that investigated SARS-CoV-2 transmission mitigation strategies in communal accommodations for people experiencing rough sleeping.
All study designs that quantitatively assessed the effectiveness of measures to protect against SARS-CoV-2 infections and COVID-19 complications in people experiencing rough sleeping in communal accommodation were included.Shared washing facilities are a common feature of 'communal accommodation' for people experiencing rough sleeping in England. 13Thus, only studies that evaluated mitigation measures in accommodations that met this definition were included.Although the structure of 'communal accommodation' may differ across countries this review aimed to evaluate the effectiveness of mitigation measures in settings similar to the provisions in England.Consequently, when evaluating the effectiveness of interventions in communal accommodation for people experiencing rough sleeping all other structural characteristics (e.g.sleeping arrangements) were considered as mitigation measures.We included modelling studies, surveillance reports, pilot studies and randomized control trials (RCTs), and excluded media articles, reviews and opinion papers.A detailed description of inclusion criteria, search strategies and terms is available in the registered PROSPERO protocol.The final search strategy did not deviate from the protocol.
Database searching was accompanied by grey literature searches and hand searching of reference lists of identified studies and publication lists of known experts.Lead researchers of ongoing relevant RCTs were contacted for potential preliminary reports or findings by the principal investigator.Title, abstract and full-text screening of all identified records were conducted independently and in duplicate by two researchers with almost perfect agreement (95%; Cohen's k = 0.88) and discrepancies were resolved through discussion.

Risk of bias assessment and data extraction
Two researchers independently assessed the risk of bias for each study using appraisal tools from the Joanna Briggs Institute (JBI). 17Two reviewers independently and in duplicate rated each domain and computed an overall risk of bias rating for each study (low, moderate and high).Discrepancies were resolved through discussions with consensuses reached on all records.Due to the anticipated low number of available literature in this review, no predefined exclusion quality cutoff was used.
Using a pre-defined and previously used 12 Excel spreadsheet, the following information was extracted for all retained records: the first author with publication year, study design, study setting/country, target population/sample, mitigation measures assessed, outcomes measured including date mea- sured and method used and main findings.Data extraction was completed independently and in duplicate by two researchers and subsequently combined, and discrepancies were independently checked by a third researcher.

Data analysis and synthesis
Due to the heterogeneity in the mitigation strategies assessed, the conceptualization of mitigation approaches and how the outcomes were reported across studies, meta-analysis was not possible here and a narrative thematic analysis was conducted.The results were organized by intervention type.

Study characteristics
We identified 883 records, including 186 duplicates through database searching.697 unique abstracts were screened and assessed for eligibility by two researchers in duplicate, of which 650 were excluded.The remaining 47 records and the 18 identified from other sources (65 in total) were sought for full-text screening.9][20][21][22][23][24][25] The remaining 14 articles were included in this review (Fig. 1).
Studies were conducted in the United States (USA), England, France, Singapore and Canada.Two studies 26,27 were longitudinal.0][41][42] Homelessness was defined inconsistently across the included studies.Nine studies included samples that contained only staff and/or residents within shelters, hostels and hotels used as emergency accommodations for people experiencing homelessness.The other five studies included additional accommodation types (e.g.squats) and/or groups of people that are living in precarious conditions (e.g.migrant workers).See Table 1, for a summary of included studies.

Population
Staff/residents in shelters/hostels/hotels for homeless people 9 Includes other accommodation and/or sub-groups of people 5 * For studies that reported on multiple outcomes, each of the outcomes was tabulated separately in this table.
efficacy of each intervention independently, not all mitigation measures were implemented in isolation (see Table 2 for more details).
The effectiveness of sleeping in single occupancy rooms and restricting resident mobility is inconsistent.Two reports from France found that sleeping in communal rooms was not associated with a higher SARS-CoV-2 infection rate or risk of hospitalization compared with sleeping in a private room, 29,30 whereas in the USA sleeping in communal rooms was associated with higher rates of positivity compared with those sleeping in a private room. 33Similarly, the effects of resident mobility varied.In a surveillance report from Canada, residents who remained in the same accommodation for 14 days were less likely to test positive. 20Conversely, in a report from France changing accommodations showed no relationship with odds of being seropositive compared with not changing accommodations. 30In France, spending less than a month in emergency shelters was associated with lower odds of being seropositive (compared with more than a month). 30In a report of six US shelters, despite implementing multiple other infection control practices (see Table 2 for details) only accommodations that prohibited new residents reported no outbreaks. 32asures reducing contact between residents also showed conflicting results.A report in France found that limiting the frequency that residents spent more than 15 min within 1 m of other residents and staff was associated with lower odds of being seropositive. 31The study reduced close contact by reducing the number of residents sharing sleeping, cooking and washing facilities.Compared with having 5 or fewer close contacts, more close contacts were associated with greater odds of testing positive for SARS-CoV-2 (6-9 close contacts: OR = 2.7, 95% CI = 1.5-5.1 and >10 close contacts: OR = 3.4, 95% CI = 1.7-6.9).This is consistent with a report from Singapore that suggested there were no reported outbreaks in homeless shelters that had increased bed spacing and staggered meal and shower times. 28However, because no further information was available in these studies it is unclear precisely how physical distancing was defined in these contexts.On the other hand, a cross-sectional surveillance report of sixty-three shelters across seven states in the USA found that increasing bed spacing to 3 feet apart and filling fewer than 74% of beds was not associated with lower SARS-CoV-2 prevalence. 34Instead, positioning beds head-to-toe and excluding symptomatic staff from working was associated with reduced odds of reporting SARS-CoV-2 prevalence  above 2.9% (the median of the 7-day average of the six counties in the study).However, it is not clear whether these shelters implemented head-to-toe sleeping and/or excluded symptomatic staff from working individually or simultaneously with other measures.

Combined measures
A cross-sectional uncontrolled pilot study 35 and two longitudinal studies 26,27 looked at a combination of measures to reduce SARS-CoV-2 transmission risk.
The strongest available evidence comes from a longitudinal report (with a low risk of bias) of four shelters (and associated hotels used for depopulation) in France that were assessed from March to November 2020. 26In this report, reducing the density of communal accommodation, encouraging good hygiene practices, and increasing social distancing helped to reduce the SARS-CoV-2 infection rate and helped to keep infection rates lower during subsequent waves of SARS-CoV-2, but did not prevent infections entirely.The study reported a decline from 21% of infected residents during the first wave of SARS-CoV-2 (March 2020) to 7% in the middle of the second wave (September 2020), following the implementation of the suggested mitigation measures. 26Similarly, a report from the USA revealed that increased accommodation cleaning, more frequent hand washing, universal mask-wearing, off-site isolation, daily symptom screening, PCR testing three times per week, and prohibiting residents who left the accommodation to return was found to reduce the SARS-CoV-2 infection rate from 45% of infected residents in April 2020 to less than 1% in May 2020. 27 Canadian uncontrolled pilot study 35 suggests that by reducing shelter density, increasing social distancing, providing rapid on-site testing, universal mask-wearing and providing an isolation area for people awaiting test results the researchers were able to keep shelter SARS-CoV-2 infection rates at 1%, which was below that of the general population (estimated 5-7%), but could not entirely stop new infections within the shelter.

Modelling studies
Three modelling studies were selected: two simulating shelters in the USA (both rated as having a low risk of bias) 36,38 and in England 37 (summarized in Table 3).
Both US studies estimated that daily symptom screening, relocation of some residents to hotels (to reduce shelter density), universal mask-wearing, off-site isolation and twice weekly PCR testing could help to reduce SARS-CoV-2 infections by between 62% 36 and 96% 38 when the reproduction number (R 0 ) is low (R 0 = 1.3 and 1.5, respectively).Under a low R 0 , it was estimated that together these mitigation measures had a 74% chance to avert an outbreak in the communal accommodation; however, as the community prevalence increases (to 2.9, 3.9 and 6.2), the effectiveness of these mitigation measures to prevent an outbreak declined to 42%, 29% and 19%, respectively. 38The simulation in England also estimated that combined packages of interventions could help dramatically reduce infection rates by 45% and hospitalizations by 92% during the first wave of COVID-19 in the country, but during the second spike in community prevalence, whilst the measures were still in place the estimated effectiveness dropped to a reduction of 24% in SARS-CoV-2 infections and 89% fewer hospitalizations.

Main findings
Existing evidence on the effectiveness of interventions to reduce SARS-CoV-2 transmission and COVID-19 complications among people experiencing homelessness in communal accommodation is weak, due to a reliance on cross-sectional study design and modelling studies as well as the risk of bias in study methodologies.However, the evidence shows that the implementation of multiple mitigation measures together can help reduce SARS-CoV-2 infections in communal accommodations, although not enough to stop all outbreaks.The pilot intervention in Canada 35 and the longitudinal surveillance report in France 26 provided the strongest evidence upon which to assess mitigation measures in this setting.Yet, many of the other studies lacked the critical information required to understand and assess the implemented interventions.Continued and better quality research into how to mitigate COVID-19 and other diseases in communal accommodation is needed, particularly taking into account how factors such as the prevalence of SARS-CoV-2 in the community can influence the effectiveness of mitigation measures.

What is already known
Communal accommodation is well recognized to increase the risk of transmission of SARS-CoV-2 12 and could accelerate the spread of other airborne pathogens, such as TB. 8 Severe complications from COVID-19 and TB are far more pronounced in vulnerable populations that have increased comorbidities and are under-vaccinated, such as people experiencing rough sleeping, migrant workers and refugees and asylum seekers. 2,43,44Differing physical, social, economic and environmental factors increase the susceptibility to hazards for each of these populations, 45 which are further exacerbated by poor living conditions. 46Thus, because it is precisely these populations that often reside in precarious housing or are living in overcrowded or communal accommodations (e.g.migrant processing centres, night shelters), 47 understanding how to protect these vulnerable populations from lifethreatening diseases in communal accommodations is crucial.

What this study adds
This review adds to the previous literature by compiling the available international evidence to assess the effectiveness of COVID-19 mitigation strategies in communal accommodations for people experiencing rough sleeping.The findings from this review suggest that implementing multiple mitigation measures simultaneously, such as early identification and isolation of positive cases, reducing accommodation density, reducing close contacts and promoting better hygiene and mask-wearing, could under some circumstances help reduce SARS-CoV-2 transmission in communal settings.Similar mitigation measures have been shown to help reduce the spread of SARS-CoV-2 in schools 48 and shelters for asylum seekers 49 and other airborne transmissible conditions, like TB 50 and influenza. 51owever, this review also exposes the weakness of the available evidence concerning assessing the effectiveness of COVID-19 mitigation measures in communal accommodations for people experiencing rough sleeping.The literature is made up of mostly cross-sectional studies that were conducted during the first wave only and before vaccine rollouts in their respective locations.Because vaccine uptake is lower in people experiencing rough sleeping 6 and some evidence suggests that there is still transmission in communal settings following vaccination, 52 it is increasingly important to understand what interventions are effective at reducing transmission risks in communal accommodations for people experiencing rough sleeping.However, with most of the available evidence being cross-sectional and many with a high risk of bias, more high-quality research that allows causality to be determined is needed to help in identifying the measures that are the most effective.
Furthermore, despite the recognition that good ventilation is likely to play a role in protecting people in communal accommodation against SARS-CoV-2, TB and Influenza, 10,50,51 no studies captured in this review assess ventilation as a mitigation measure in communal accommodation for people experiencing rough sleeping.
Finally, this review demonstrates that factors such as community prevalence can influence how effective different mitigation measures are.For instance, a modelling study estimated that universal mask-wearing on its own would reduce the infection rate in the shelter by 86% when the community prevalence was low, but only by 56% when community infection rates were high.This is important because during periods of low community prevalence individual mitigation measures may be sufficiently effective.France and Canada's national lockdown was stricter than in the USA, 53 where large social and religious gatherings still occurred. 54Thus, national policies and behaviours and attitudes of residents in the surrounding communities may also influence the effectiveness of mitigation measures.

Limitations of study
There are, however, some caveats of this review that need to be considered.To begin with, this review did not include pre-print servers which may have resulted in some available evidence being missed.Additionally, the study designs of the literature captured by this review are too limited to allow concrete recommendations on individual mitigation measures for policymakers and accommodation providers to be provided.Finally, variability in the types of communal accommodations reported on and the country-level differences in the COVID-19 landscapes in the captured studies make relating the findings from this review to the UK setting more difficult.

Conclusions
This review reveals that the available evidence to assess the effectiveness of COVID-19 mitigation strategies in communal accommodations for people experiencing rough sleeping is weak.Yet, together it suggests that even though no intervention or 'package of interventions' is likely to prevent outbreaks, they can be used to reduce SARS-CoV-2 infections and COVID-19 complications in this setting.Combining the opening of additional accommodations to reduce the density in communal shelters, universal mask-wearing and proper hygiene practices (i.e.hand washing, less face touching, and good coughing etiquette) may help reduce infection rates in communal accommodations for people experiencing rough sleeping.However, the evidence also suggests that situational factors such as community prevalence will play a role in the efficacy of implemented mitigation packages.It is unclear whether other individual or combinations of mitigation strategies not assessed here could prevent outbreaks or further reduce infection risks in communal accommodations for people experiencing rough sleeping.Thus, better quality research is urgently needed in this area.

Table 1
Characteristics of synthesized studies *Infection incidence/transmission risk or rate 13Number of and severity of outbreaks 2

Table 2
Summary of synthesized surveillance studies